1. Field of the Invention
This invention relates to a fuel supply apparatus, and more particularly to a fuel supply apparatus for supplying a fuel under a high pressure to a fuel injection type internal combustion engine, for example, an automobile engine.
2. Description of the Related Art
FIGS. 7-9 are drawings for describing a general fuel supply system for a fuel injection type internal combustion engine. FIG. 7 schematically illustrates this fuel supply system. FIG. 8 is a sectional view of a principal portion of a fuel supply apparatus included in the same fuel supply system, and FIG. 9 an enlarged sectional view of a part of what is shown in FIG. 8. Referring to FIGS. 7-9, the fuel supply system has as main elements a fuel tank 1, a fuel supply apparatus 6 and fuel injection valves 10, the fuel supply apparatus 6 having a filter 11, a low-pressure damper 12, a suction valve 13, a pump 16, a discharge valve 14 and an electromagnetic valve 40.
A fuel 2 in the fuel tank 1 is sent out by a low-pressure pump 3, and pressure-regulated in a low-pressure regulator 5 via a filter 4, the resultant fuel being supplied to the fuel supply apparatus 6. The pressure of only such a quantity of the fuel 2 thus supplied to the apparatus that is necessary for fuel injection is increased to a high level by the same apparatus 6, and the resultant fuel is supplied to the interior of a common rail 9 of an internal combustion engine (not shown). The fuel is then injected in the form of a high-pressure mist from the fuel injection valves 10 into cylinders (not shown) of an internal combustion engine. A necessary quantity of the fuel during this injection operation is determined by a control unit (not shown), and controlled by the electromagnetic valve 40, an excessive fuel being relieved from the electromagnetic valve 40 to the portion of a fuel passage which is between the low-pressure damper 12 and suction valve 13. A reference numeral 7 in FIG. 7 denotes a filter, and 8 a high-pressure relief valve. When the interior of the common rail 9 comes to have an abnormal pressure, the high-pressure relief valve 8 is opened to prevent the common rail 9 and fuel injection valve 10 from being broken.
Referring to FIG. 8 showing a principal portion of the fuel supply apparatus 6, the pump 16 includes a cylinder 25 installed in a casing 30 and provided therein with a pressure chamber 24 having a fuel suction port 22 and a fuel discharge port 23, a plunger 26 adapted to be moved vertically in the interior of the cylinder 25 and thereby vary the volume of the pressure chamber 24, and tappet 28 joined to the plunger 26. A driving cam (not shown) provided coaxially with an engine cam shaft (not shown) is engaged with a pressure receiving surface at a lower end in the drawing of the tappet 28, and the tappet 28 and plunger 26 are moved vertically in accordance with a rotation of this driving cam to cause the volume of the pressure chamber 24 to be varied.
Referring to FIGS. 8-9, the electromagnetic valve 40 has a core 41 and an electromagnetic coil 42, and is fixed to a housing 43. The core 41 and housing 43 are welded together via a connecting ring 50 having an L-shaped cross section. Namely, the connecting ring 50 has a first portion 51 welded to the core 41, and a second portion 52 welded to the housing 43. In other words, the core 41 and first portion 51 are welded at a welded portion 61, and the housing 43 and second portion 52 at a welded portion 62 respectively. In FIG. 9, an illustration of the electromagnetic coil 42 is omitted so that such welded condition is understood easily.
In order to connect the core 41 and housing 43 together, the connecting ring 50 is press fitted therebetween first, and each abutting portion is welded over the whole circumference thereof by a regular method to form the welded portions 61, 62.
The welded portions 61, 62 contract while they cool down after the welding operation finishes, and the connecting ring 50 of a low strength is deformed so as to be drawn to the core 41 and housing 43 as shown by arrows in FIG. 9, i.e., in such a manner that the first and second portions 51, 52 thereof are drawn toward the core 41 and housing 43 respectively. The degree of this deformation is not uniform from a welding starting position toward a welding finishing position in the circumferential direction of the connecting ring 50. As a result, an abominable problem arises, i.e., the core 41 inclines with respect to the axis thereof to cause the performance of the electromagnetic valve 40 to become unstable.
In the welded portions 61, 62, especially, in the welded portion 62, stress including a large tensile component resides on the surface thereof due to the above-mentioned contraction thereof, and this residual stress causes a crack to occur in the welded portion 62. The connecting ring 50 in use is formed in many cases of a nonmagnetic steel material, for example, stainless steel of austenite. Since the linear expansion coefficient of this material is larger than those of other metal materials, the problems mentioned above stand out more. Furthermore, when a pressure is applied to the interior of a fuel passage of the electromagnetic valve 40, a clearance occurs between contact surfaces of the connecting ring 50 and housing 43, especially, in the radial direction due to the deformation mentioned above of the connecting ring 50. The above-mentioned pressure works in such a clearance, and a pressure receiving area gradually increases, the degree of deformation of the connecting ring also increasing. Therefore, there is the possibility that fatigue failure occurs in the above-mentioned deformed portions during an operation of the electromagnetic valve 40 to give rise to the leakage of the fuel.
The present invention has been made in view of the above-mentioned circumstances, and provides a fuel supply apparatus which has solved the problem occurring after the welding of a connecting ring, by which a core of an electromagnetic valve and a housing are connected together, finishes of the deformation of the connecting ring and a crack in a welded portion.
According to an aspect of the present invention, the fuel supply apparatus has a core of an electromagnetic valve and a housing which are welded together via a connecting ring having an L-shaped cross section, the housing being provided in the portion thereof which is in the vicinity of the part of the housing on which the housing is welded to the connecting ring therefor with a groove for at least reducing the degree of deformation of the connecting ring occurring after the welding operation finishes.
According to another aspect of the present invention, the fuel supply apparatus is in accordance with the above invention, in which the connecting ring has a first portion welded to the core, and a second portion welded to the housing, the thickness of the second portion being larger than that of the first portion.
According to still another aspect of the present invention, the fuel supply apparatus is in accordance with the second-mentioned invention, in which the thickness of the second portion is larger than the depth of a cut made in a corner of the housing and adapted to have the second portion fitted therein.
According to a further aspect of the present invention, the fuel supply apparatus is in accordance with the first-mentioned invention, in which an open surface of the welded portion of the housing and connecting ring project in a swollen state.
According to another aspect of the present invention, the fuel supply apparatus is in accordance with any one of the first to fourth inventions, in which the groove is cross-sectionally so shaped that the distance between both of opposite side walls thereof decreases gradually toward a bottom thereof.
According to still another aspect of the present invention, the fuel supply apparatus is in accordance with the fifth-mentioned invention, in which the side surface of the groove which is on the side of the connecting ring has an angle of inclination of 40-60 degrees.